a) Field of the Invention
The present invention relates generally to brake controlling apparatus and method for executing an anti-lock brake control (hereinafter, also called ABS control) to prevent a wheel""s lock by controlling a corresponding brake pressure during a braking operation and, particularly, to a technique of calculating arithmetically control-purpose wheel accelerations (decelerations) to be used for a braking liquid pressure decrease control.
b) Description of the Related Art
When the ABS control is executed in a brake control system, a previously proposed brake system determines road wheel velocities under control (hereinafter, referred to as control-purpose wheel velocities) of respective road wheels (front left and right road wheels and rear left and right road wheels) or the front left and right road wheels and one rear road wheel velocities), calculates a pseudo vehicular body velocity approximated to a vehicular running velocity from these control-purpose road wheel velocities, calculates a pressure decrease threshold value which is a road wheel velocity corresponding to a most appropriate velocity of the vehicle on the basis of the pseudo vehicular body velocity, and decreases the pressure of a corresponding wheel cylinder when the control-purpose road wheel velocity of the road wheel to be controlled is in excess of a pressure decrease threshold value so as to prevent the wheel""s lock. If is also known that when the control-purpose road wheel velocity is generated, one of the four road wheels is selected from among the plurality of road wheels on the basis of a previously set condition and a select processing such as to set the road wheel velocity of the selected road wheel as the control-purpose road wheel velocity is carried out.
During the braking, the previously proposed brake control system determines a gradient of the pseudo vehicular body velocity on the basis of an acceleration of the pseudo vehicular body velocity and uses the control-purpose road wheel acceleration which is a differentiation of the control-purpose road wheel velocity of one rear road wheel with respect to time to the calculations such as the pressure decrease quantity of each road wheel. This is exemplified by a Japanese Patent Application First Publication No. Heisei 9-207745 published on Aug. 12, 1997.
It is noted that the above-described select processing includes, for example, a rear road wheel select low, an diagonal select low, a triangular select low, and a triangular select.
These select processing will briefly be explained below.
The rear road wheel select low is such that the control-purpose rear road wheel velocities VwRR0 and VwRL0 are selected from one of the values of the road wheel velocities VwRR and VwRL which is smaller than the other, viz., VwRR0 (VwRL0)=min {itself road wheel velocity Vw, the other road wheel velocity on the same axle Vw}.
The diagonal select low is such that the control-purpose rear road wheel velocity to be controlled is selected from either one of one of the rear road wheel velocities and one of the front road wheel velocities, both of which are in the same diagonal line, which is smaller than the other, viz., VwRR0 (VwRL0)=min {itself road wheel velocity Vw, and diagonal front road wheel velocity Vw}.
For example, if the object to be controlled is the rear left road wheel RL, a rear left road wheel controlling road wheel velocity VwRLO is selected from either one of the rear left road wheel. velocity VwRL or the front left road wheel velocity VwFL which is smaller than the other.
The triangular select low is such that any one of the values of the own vehicular velocity, the other road wheel velocities which is in the same axle line, and the diagonal front road wheels which is smallest than the other.
That is to say, VwRR0 (VwRL0)=min {itself road wheel velocity Vw, diagonal front road wheel velocity Vw}. For example, if the object to be controlled is the rear left road wheel RL, the brake control system sets one of the rear left road wheel velocities and the front right road wheel velocity VwRL and VwFL which is smaller than the other as the rear right road wheel control-purpose wheel velocity VwRL0.
The triangular select is such that either one of the diagonal front road wheel velocity and the same axle other wheel velocity which is larger than the other and either one of the larger value of the diagonal front road wheel velocity and the same axle other road wheel velocity which is smaller than the other and the rear road wheel control-purpose road wheel velocity, viz., max {the same axle other wheel velocity Vw, diagonal front road wheel velocity Vw}}. For example, if the object to be controlled is the rear left road wheel RL, the brake control apparatus, for example, sets the larger value of the rear right road wheel velocity VwRR and the front right road wheel velocity VwRF to be the rear left road wheel control-purpose wheel velocity VwRL0 if the object to be controlled is the rear left road wheel RL.
However, in the previously proposed brake control system, the rear road wheel control purpose road wheel acceleration is determined by differentiating the rear road wheel control-purpose wheel velocity with respect to time generated by means of the previously determined rear road wheel select low, the diagonal select, the triangular select low, and the triangular select.
Hence, in a case where the selected road wheel is sequentially varied, the control-purpose road wheel acceleration is calculated with the road wheel to be selected switched. Hence, a sufficient time to determine a variation rate of the road wheels to be selected with a high accuracy cannot be obtained. Such a problem occurs that only the control-purpose wheel acceleration with a low accuracy can be obtained or the control-purpose wheel acceleration indicates an excessively small value. In addition, such a problem occurs that if the control-purpose wheel acceleration is not calculated until a time to obtain the highly accurate control-purpose wheel acceleration has passed, a retardation of a control responsive characteristic occurs. Furthermore, in a case where the control-purpose road wheel acceleration indicates the excessively small value, the pressure decrease quantity is set to be excessively small. Due to a lack in pressure decrease quantity, the pseudo vehicular body velocity indicates the smaller value than the actual one so that a rear road wheel cornering force is reduced and a controllability is worsened.
It is therefore an object of the present invention to provide vehicular brake controlling apparatus and method for selecting a single road wheel velocity from a plurality of road wheels through a predetermined select processing to determine a rear road wheel control-purpose wheel velocity (or velocities), for determining the rear road wheel control-purpose wheel acceleration (or accelerations) with the high accuracy and high responsive characteristic even if the switching of the selected road wheel is carried out, and for preventing the retardation of the control responsive characteristic, and which can provide an appropriate quantity of the braking liquid pressure decrease, and can improve a control quantity.
The above-described object can be achieved by providing a vehicular brake controlling apparatus comprising: a brake unit arranged to enable an independent control of braking liquid pressures for respective wheel cylinders to brake their corresponding road wheels of the vehicle; a plurality of road wheel velocity sensors to detect respective wheel velocities of the road wheels of the vehicle, the road wheels being front left and right and rear left and right road wheels; and a controller, the controller including: a road wheel acceleration calculating section to calculate road wheel accelerations of the respective road wheels from respective road wheel velocity values detected by the road wheel velocity sensors; a road wheel velocity select processing section to select any one of the road wheel velocities including the road wheel velocity of one of the road wheels that is an object to be controlled in an anti-lock brake control during a brake operation on the basis of a predetermined condition, the selected road wheel velocity serving as a control-purpose road wheel velocity; a control-purpose road wheel acceleration generating section to select any one of the road wheel accelerations from among results of calculations of the road wheel accelerations by means of the road wheel acceleration calculating section which corresponds to one of the road wheel velocities which is selected by the road wheel velocity select processing section so as to generate a control-purpose road wheel acceleration; and an anti-lock brake controlling section to execute the anti-lock brake control for each road wheel through the brake unit during the brake operation using the control-purpose road wheel velocity and the control-purpose road wheel acceleration so as to prevent a wheel""s lock for each road wheel from occurring.
The above-described object can also be achieved by providing a brake controlling method for an automotive vehicle, the vehicle including: a brake unit arranged to enable an independent control of braking liquid pressures for respective wheel cylinders to brake their corresponding road wheels of the vehicle; a plurality of road wheel velocity sensors to detect respective wheel velocities of the road wheels of the vehicle, the road wheels being front left and right and rear left and right road wheels; and a controller, the brake controlling method comprising the steps of: calculating road wheel accelerations of the respective road wheels from respective road wheel velocity values; selecting any one of the road wheel velocities including the road wheel velocity of one of the road wheels that is an object to be controlled in an anti-lock brake control during a brake operation on the basis of a predetermined condition, the selected road wheel velocity serving as a control-purpose road wheel velocity; selecting any one of the road wheel accelerations from among results of calculations of the road wheel accelerations which corresponds to one of the road wheel velocities which is selected so as to generate a control-purpose road wheel acceleration; and executing the anti-lock brake control for each road wheel through the brake unit during the brake operation using the control-purpose road wheel velocity and the control-purpose road wheel acceleration so as to prevent a wheel""s lock for each road wheel from occurring.